1. Quarter 1 Unit 2 “Atomic Structure”
Defining The Atom

2. Early Models of the Atom
Atom: the smallest particle of an element
The Greek philosopher Democritus (460 B.C. – 370 B.C.) was the first to suggest the existence of atoms
He believed that atoms were indivisible and indestructible
His ideas were not based on experiments, just philosophy

3. Lavoisier: The Law of Conservation of Mass
Changed chemistry to a quantitative science
Measured the mass of a system before and after a reaction in a closed system
Stoichiometry
Isolated and named hydrogen and oxygen
Discovered how respiration and combustion are related
Major experiment involved cinnabar: red mercury oxide

4. Lavoisier’s Cinnabar Experiment

5. Proust: The Law of Definite Proportions
Copper carbonate from a variety of sources
Lab-made was 57.48% Cu, 5.43% C, 0.91% H, and 36.18% O
Natural was 57.48% Cu, 5.43% C, 0.91% H, and % O

6. Definite Proportions
A compound always contains the same elements in certain, definite proportions
Also known as the law of constant composition

7. Dalton’s Atomic Theory
~2000 years pass before more was known about the atom
John Dalton; English Chemist & School teacher; 1803
Thought the atom looked like a marble.(Round, solid sphere)
His findings were based on scientific experiments, not philosophy

8. Dalton Dalton (1803) Known as the FOUNDER of the atomic theory
Dalton invented the word ATOM as the basic unit of matter
Dalton also claimed that all atoms of a given element are IDENTICAL
He also discovered that atoms of different elements have different PROPERTIES AND MASSES
Found that combining atoms of different elements formed COMPOUNDS

9. Dalton’s Postulates Compounds are composed of elements
Atoms of the same elements are identical and differ from other elements.
Atoms chemically combine in whole-number ratios
Atoms cannot be created or destroyed

10. Sizing up the Atom
Atoms are extremely small
A penny containing pure copper contains 2,400,000,000,000,000,000,000,000 atoms
Population of our planet: ~6,000,000,000
If you could line up 100,000,000 copper atoms in a single file, they would be approximately 1 cm long
Can only be observed using a scanning tunneling (electron) microscope

11. SEM Microscope

13. Dmitri Mendeleev 1869
Arranged elements into 7 groups with similar properties.  He discovered that the properties of elements  "were periodic functions of their atomic weights".  This became known as the Periodic Law.

14. Crookes Tube (CRT)

15. A magnet will deflect the cathode ray
Particles in the cathode ray are negatively charged

17. J.J. Thomsom 1897
While using a CATHODE RAY TUBE he discovered that the ray was deflected (due to a magnetic/electrical field
From this discovery he concluded that atoms contain small negatively charges particles called ELECTRONS
Theory famously referred to as the PLUM PUDDING model because he visualized the ELECTRONS being EMBEDDED within the structure of the atom (just like raisin bread)
The MASS of the rest of the atom (besides the electrons) was thought to be EVENLY DISTRIBUTED and POSITIVELY CHARGED

18. Thomson’s Atomic Model
“Plum Pudding” model: the electrons were like plums embedded in a positively charged “pudding,”
J. J. Thomson

19. The philosopher who first suggested the existence of atoms was ____________.
John Dalton
Democritus
Ernest Rutherford

20. The three subatomic particles that make up an atom are .
proton, neutron, electron
nucleus, proton, electron
cathode rays, canal rays, neutrons

21. True or False? A Scanning Tunneling Electron Microscope is the only device we can use to see atoms.

22. John Dalton’s model of the atom looked like a ___________
soccer ball
marble
football

23. Democritus believe that atoms were _____
Indivisible & Invisible
Indestructive & Invisible
Indivisible & Indestructive

24. True or False? There were only ~200 years between Democritus’ theory and John Dalton’s work with the atom.
True
False

25. The scientist who discovered the electron was _____________
JJ Thomson
Robert Millikan
Ernest Rutherford

26. Mass of the Electron
The oil drop apparatus
Mass of the electron is
9.11 x g
1916 – Robert Millikan determines the mass of the electron: 1/1840 the mass of a proton

27. Goldstein (1886) Discovered the “Proton”
Goldstein proved that when negative particles are formed, so are positive
These positive particles were found to have a mass 1837x that of an electron

28. discovered the “neutron”
932 – James Chadwick (1932)
discovered the “neutron”
a particle with no charge, but a mass equal to a proton

29. Ernest Rutherford In 1911, Designed the Gold Foil Experiment
Aimed a beam of alpha (α) particles at a thin piece of gold foil (only a few atoms thick.)
Most α particles passed through the foil…
A small amount of the α particles
were deflected
To their surprise, some α particles
bounced straight back.
1 in ~8000 did not go through the foil

30. Alpha Particle Experiment

31. Actual Results Most went straight through
Mostly empty space
Some were deflected at huge angles
Positive charge in center of atom
Others bounced straight backwards!!
Small, dense solid area in center of atom
Nuclear Model

32. A Visual Example

33. Rutherford’s Atomic Model

34. The nucleus is positive Atoms are mostly empty space
Conclusions:
There is a nucleus in the center of the atom where most of its mass is.
The nucleus is positive
Atoms are mostly empty space
Disproved J.J. Thomson’s Plum Pudding Model
If an atom is the size of a football stadium, the nucleus is the size of a marble

35. Niels Bohr 1885-1962 Planetary Model 1913
Nucleus surrounded by orbiting electrons at different energy levels
Electrons have definite orbits
Utilized Planck’s Quantum Energy theory
Worked on the Manhattan Project (US atomic bomb)

36. Bohr Model for Nitrogen

37. Electrons, protons, and neutrons
Change to Dalton’s atomic theory: atoms are divisible into subatomic particles:
Electrons, protons, and neutrons

38. Subatomic Particles Particle Charge Mass Location Electron (e-) -1
virtually nothing
cloud
Proton +1 1
Nucleus
Neutron

39. # protons in an atom = # electrons
Atomic Number
Elements are different because they contain different numbers of PROTONS
atomic number = the number of protons in the nucleus
# protons in an atom = # electrons

40. Mass Number
Mass number = number of protons and neutrons in the nucleus
Mass # = p + n
Element p n e
Mass #
Oxygen - 8 - 33 42
- 31 15 16 8 8 16
Arsenic 75 33 75
Phosphorus 16 15 31

41. Nuclide Symbols
Contain the symbol of the element, the mass number and the atomic number.
Atomic
number X
Superscript →
Mass
number
Subscript →

42. Br Symbols 35 80 Find each of these: number of protons
number of neutrons
number of electrons
Atomic number
Mass Number 35 Br 80

43. Symbols
If an element has an atomic number of 34 and a mass number of 78, what is the:
number of protons
number of neutrons
number of electrons
complete symbol

44. Symbols
If an element has 91 protons and 140 neutrons what is the
Atomic number
Mass number
number of electrons
complete symbol

45. Symbols
If an element has 78 electrons and 117 neutrons what is the
Atomic number
Mass number
number of protons
complete symbol

46. Isotopes
Atoms of the same element can have different numbers of neutrons.
Thus, different mass numbers.
Isotopes change the number of neutrons & the mass number for an atom

47. Frederick Soddy proposed the idea of isotopes in 1912
Isotopes: atoms of the same element having different masses, due to varying numbers of neutrons.
Elements occur in nature as mixtures of isotopes.

48. Element name – mass number:
Naming Isotopes
Element name – mass number:
carbon-12
carbon-14
uranium-235

49. Hydrogen–1 1 (protium) Hydrogen-2 (deuterium) Hydrogen-3 2 (tritium)
Isotope
Protons
Electrons
Neutrons
Nucleus
Hydrogen–1
(protium) 1
Hydrogen-2
(deuterium)
Hydrogen-3
(tritium) 2

50. Atomic Mass
The Gold number on the P.T. is the Average Atomic Mass of the element
This is based on the abundance of each variety of that element in nature.
Instead of grams, the unit we use is the Atomic Mass Unit (amu)
It is defined as one-twelfth the mass of a carbon-12 atom.

51. The Periodic Table: A Preview
Each horizontal row is called a period
Each vertical column is called a group, or family
Elements in a group have similar chemical and physical properties